Network switches play a critical role in large computer networks, such as those found in a data center. Server computers in the network can be divided into racks, and network switches can connect the server computers within a rack to routers in the data center. Data passed by switches is generally divided into a series of packets that can be transmitted between devices. Generally, network switches have two primary planes: a control plane and a data plane. The control plane is a management plane that configures the data plane. The data plane receives packets on input ports and transmits the received packets to output ports based on the configuration. Both the data plane and the control plane can become non-functional for a number of reasons. For example, a processor crash can occur, or other hardware or software malfunction. Any of these events can cause the entire switch to be offline for an extended period. For example, the control plane operating system may need to go through a boot operation before the switch can become operational again. As a result, neighbor routers that stop receiving announcements from the switch can remove the switch from their forwarding tables. Multiple users of the network can therefore be impacted by a switch outage if the users are executing software on a server computer that receives network traffic through the switch.
Before the switch is taken offline for servicing, the network traffic is diverted until the traffic to the switch is below a threshold level. However, any changes to the network switch, including changes of the data plane forwarding tables or the control plane state, can result in masking of a defect in the network switch making the switch more difficult to troubleshoot.